Pitch paint



Patented July 12, 1938 UNITED STATES PATENT oFiucE No Drawing.Application August 14, 1934, Serial No. 739,841

2 Claims.

This invention covers a pitch paint that is an improvement over otherpaints of this character respecting its elastic and adhesive properties.

This paint includes coal tar pitch and a mix- 5 ture of coal tar oilshaving boiling points of from 100 to 300 degrees centigrade, and issubstantially free of tar acids and other acidic compounds as well ascoal tar oils boiling above 300 degrees centigrade. Approximately 60 percent of this mixture boils below 210 degrees centigrade, and the mixturecontains some naphthalene and a relatively small percentage ofpoly-phenols. The 1 pitch used is characterized in that it is producedfrom 100 per cent washed Pittsburgh bituminous coal.

The coal tar oils mentioned carry the pitch in practically truesolution. The naphthalene and poly-phenols function to impart elasticand adhesive properties, and the pitch described is of particular valueas it is found to have a low percentage of free carbon which is alwaystroublesome since it tends to segregate rather than to remain evenlysuspended in the paint.

Most pitch paints consist of coal tar pitch carried in a more or lesscolloidal state by solvent naphtha of which 90 per cent distills below210 degrees centigrade, or of coal tar pitch, a coal tar solvent and atar acid. The first type is subject to the difficulty that the pitchcannot be kept in a dispersed condition, while the second type may alsobe subject to this trouble and, in addition, is corrosive and does nothave sufiicient adhesive and elastic properties.

In manufacturing the paint covered by the present invention, washedPittsburgh bituminous coal is coked and the coal tar is recovered fromthe products of this process. The washing of the coal causes the fineparticles to be wet so that they are not carried over with the coke-ovengases, which are therefore relatively low in free carbon. Furthermore,the water in the washed coal lowers the temperature of the oven gases soas to retard cracking of the gases in the coking operations. The pitchis then obtained from products of this operation by means of rapiddistillation in the continuous tube still. By this method the pitch isnot subjected to excessive temperatures, which further assures theproduction of a pitch that is relatively low in free carbon. The pitchthus produced is found to have a free carbon content not exceeding 10per cent.

The light oils resulting from this distillation which boil between 100and 300 degrees centigrade are then treated with a weak solution ofsodium hydroxide so as to remove the tar acids and the acidic compounds.This solution is sufiiciently weak to leave from .5 to 1.0 per cent ofthe poly-phenols in the oils. Also, a known quantity of naphthalene,about 25 per cent, is left in the oils.

Although the color of these oils has no particular bearing on theultimate paint it is desirable to use the darker colored oils since theyhave been found to have a certain small amount of natural gum formationwhich remains as a portion of the paint film and acts as an additionalbinder for the residual pitch.

These light oils are generally separated into two fractions, one ofwhich has a boiling point range of from 210 to 300 degrees centigradeand the other of which has a boiling point range of from 100 to 220degrees centigrade, to per cent of which boils below 210 degreescentigrade. These fractions are formed into a mixture so as to produce asolvent having a boiling point range of from to 300 degrees centigrade,approximately 60 per cent of which boils below 210 degrees centigrade.The treatment with the sodium hydroxide is suiiicient to reduce the taracids and the other acidic compounds so that the oils contain not morethan 1 per cent of the same.

This mixture is placed in a tank while still hot and a measured amountof liquid pitchis added While agitating the oils. The proportions of themixture and pitch are varied, depending upon the melting points of thepitch and the fluidity required in the final product. The result is thedesired paint.

I claim:

1. Paint including coal tar pitch and a mixture of coal tar oils havingboiling points of from 100 to 300 degrees centigrade and which issubstantially free of tar acids and other acidic compounds, said paintbeing substantially free of coal tar oils boiling above 300 degreescentigrade and approximately 60 per cent of said mixture boiling below210 degreescentigrade.

2. Paint including coal tar pitch and a mixture of coal tar oils havingboiling points of from 100 to 300 degrees centigrade and which issubstantially free of tar acids and other acidic compounds, said paintbeing substantially free of coal tar oils boiling above 300 degreescentigrade and approximately 60 per cent of said mixture boiling below210 degrees centigrade, said mixture containing some naphthalene and arelatively small percentage of poly-phenols.

GEORGE W. BENNETT.

